The present invention relates to the general subject of power windows, and more particularly, to a system and method for determining torque in a window lift mechanism.
Power windows are standard equipment in many vehicles manufactured at the present time. An important problem in power window systems relates to pinch force, which is defined as the force that is exerted upon an obstruction (e.g., a person""s hand or head) that is introduced between the window glass and the window frame while the window is closing. One accepted specification is that, while the window gap (i.e., the distance between an upper edge of the window glass and a corresponding top portion of the window frame) is between 4 millimeters (mm) and 30 mm (i.e., the pinch region), the pinch force must not exceed 100 newtons.
In some existing power window systems, the shaft of the electric motor driving the window generally rotates too fast to be stopped in time to avoid exceeding a 100 newton pinch force. This is a consequence of the fact that conventional power window motors have considerable inertia and thus do not slow down instantaneously. Therefore, to avoid exceeding the maximum allowable pinch force, it is necessary that the window speed be limited while the window is being raised through the pinch region.
One approach is to simply hold the speed at a constant low level over the full range of travel. Unfortunately, this approach has the disadvantage of significantly increasing the amount of time it takes to close the window, which can be a major inconvenience (e.g., upon leaving a toll booth). Additionally, in many prior art systems, the speed at which the window closes is critically dependent upon the battery voltage, which can vary over an appreciable range. For example, in systems that close the window at a uniform speed (which must be relatively low in order to satisfy anti-pinch requirements), a reduction in battery voltage has the undesirable effect of further decreasing the already low speed at which the window closes.
Another problem exists in current based systems. Namely, such systems do not work well during window start and stop situations. Accordingly, there is a need for a window lift control system that can accurately determine a pinch condition, even during start and stop conditions.